I think the primary problem is that you just aren't getting water circulation around those roots- they're too packed. o2 rich water is just shunting around your incredibly dense rootball.

(See what happens when you let a powerplant eat all it wants?)

Anyway, it does kinda look like there may be a secondary pathogen issue- hopefully just psuedemonas shlurping up what ever 02 is making it to your roots, cause that's fixable.

Do the roots near the core feel kind of slimy?

I'd try to loosen up the rootball by hand and use my fingers to comb out any diseased tissue- I'm betting you've got a lot of semi-necrotic tissue in there that'll pop right out. It's nothing but a res of pathogens @ this point.

You could try boosting the o2 w/ some peroxide as well.

The wilt looks more like rhictozoma than pythium to me- but that's a pretty academic differance.

Seriously, with any luck it's just an aerobic slimecoat thing, and a little hand agitation and a good rinsing out will fix it.

This is gonna sound extreme, but have ya thought about physically inserting an airstone right into the center of that rootball? I mean, yeah, it's gonna shock the roots a little bit, but if it's intubation or suffocation, well, easy choice...

And def try the peroxide... Seen it stave off rhicto long enough to get out clean, if that's the problem.